// Initialise pins
int led_pin = 13;
int btn_pin = 12;

// Initlise value
int btn_value = 0;

void setup() {
  pinMode(led_pin, OUTPUT);
  pinMode(btn_pin, INPUT);
}

void loop() {
  // read button
  btn_value = digitalRead(btn_pin);
  
  if (btn_value != 0){
    digitalWrite(led_pin, HIGH);
  } else {
    digitalWrite(led_pin, LOW);
  }
}